This invention relates to lighting fixtures, and more particularly to fluorescent lampholder fittings which are adapted to screw into portable lamps and lighting fixtures. Fluorescent light sources which are adapted to replace an incandescent lamp in portable lamps and lighting fixtures are currently known and have become widely used since the introduction of products based on the applicant's U.S. Pat. No. 4,016,020 for a circline fluorescent lampholder fitting, and U.S. Pat. No. 4,015,276 for a fluorescent lampholder to connect a circline fluorescent lamp to a male screw base housing. Further, certain fluorescent lampholder fittings have been marketed that employ solid-state ballasts which have improved efficiency over the more commonly used inductor ballasts. Solid-state fluorescent ballasts typically employ an AC-to-DC converter and an inverter circuit of a single or multi-level output, which may be illustrated by the applicant's U.S. Pat. No. 3,215,723, capable of providing lamp and filament heater current from a tapped secondary transformer winding.
Recently disclosed is the applicant's U.S. Pat. No. 4,178,535 which teaches the use of multi-level fluorescent lamp operation using the built-in selective switching of a three-way lampholder of a portable lamp or lighting fixture, and using a plurality of inductor windings to control lamp current and therefore brightness. The practicality of utilizing fluorescent light sources in incandescent lampholders (sockets) was further enhanced by the teaching of the applicant's U.S. Pat. No. 4,198,112 showing torque-limiting male screw bases in both one-way and three-way brightness configurations.
It is noted that there are currently-known three-way brightness solid-state ballasted fluorescent lampholder fittings. However these devices provide the brightness control through a separate switch on the lampholder fitting, and do not utilize the three-way switching capability of the lampholder of the portable lamp supporting the fitting. At the present time nearly all of the portable lamps sold for residential use employ three-way lampholders. The availability of high efficiency fluorescent converters which are suited to the switching system built into the lamps, and to which the user is accustomed, is important to market acceptance of energy efficient residential lighting products.